THE TOTAL SOLAR ECLIPSE OF APRIL 6, 1875. 
151 
minences is rather more than 6', hence the continuous spectrum extends at least 
to a distance of 3' from the sun. The continuous spectrum is well shown on 
the photographs, figs. 8 and 9, taken at the beginning and end of the eclipse 
respectively. One of the plates in the prismatic camera was exposed during the last 
part of the eclipse until the signal for the end of totality was given. All the 
observers agreed in saying that the signal was given rather too late, and the fogginess 
of the plate indicates the great intensity of the light. Yet the edge of the sun is not 
drawn out into a continuous band, but rather into three distinct bands, showing that 
at the time of exposure the lower part of the chromosphere only had appeared. 
These lower parts gave out light of such intensity that to all observers it appeared as 
if the body of the sun had come out. 
A series of rapid photographs taken at beginning and end of totality would no 
doubt give most interesting results. 
VII. RESULTS OF THE SPECTROSCOPIC CAMERA. 
Arrangements were made to photograph the spectrum of the prominences and 
corona by means of a camera attached to a spectroscope. No results were obtained, 
and we must, therefore, discuss the reason of this failure, and see whether the instru- 
ments can be improved in such a way as to give a fair chance of success in other 
eclipses. The light of the corona no doubt is very feeble, but considering that the 
prismatic camera has given good photographs in one minute, and that we have 
obtained direct photographs of the corona in two seconds, success is not out of 
question. Even the instruments used during the last eclipse have not had a fair trial. 
Owing to delays on the journey only one day could be given to the adjustments of the 
instruments, and as the spectroscopes had never been used before they could not in 
that time be brought into the best possible state. It was, indeed, found that all the 
collimators were too long. As they could not be made shorter without considerable 
delay, the cameras had to be adjusted for the rays which were converging as they 
passed through the prism. This, of course, damaged much the definition of the image, 
especially as the prisms were made of quartz. In order to obtain a reference spectrum 
the cusp of the reappearing sun was thrown on the slit and exposed for about 15 
seconds. Yet even this reference spectrum did not appear, showing that the instru- 
ment must have been out of order. The focal length of one of the cameras used was 
too large, yet the other ought to have given results had the image of the corona been 
bright enough. This camera was attached with its spectroscope to the only equatorial 
available for use for the purpose ; it was kindly lent to the expedition by Mr. Penrose. 
The proportion of the aperture to the focal length in this instrument is 1 : 16. This 
proportion in the reflecting telescope used by Dr. Janssen is 1:4, it has, therefore, 
16 times as much fight as that used by the English expedition. The observations to be 
made during total solar eclipses have arrived at such a point that a successful attack 
